The present invention relates to filter systems, and in particular, to an improved permanent filter system incorporating an integral backflush means which may, if desired, be utilized as an insert to retrofit pre-existing pressure vessels.
Many fluid handling systems require a filter system to remove contaminants from the fluid being handled. As is well known in the art, a variety of filter media are available for the purpose. The filter material may be temporary in nature such as, for example, diatomaceous earth or powdered ion exchange resin, which forms what is known as a "precoat" that is commonly packed around or supported on apertured hollow pipes or the like. Alternatively, the filter may be permanent in nature, such as porous sintered metal or compressed stacks of discs, each formed on at least one face with passages, sometimes referred to as edge filtration filters. In some critical applications, the filter medium must be housed in expensive pressure vessels meeting the requirements of the ASME Boiler and Pressure Vessel Code as in, for example, nuclear power stations. While not so limited, the present invention has special utility in filter systems of the pressurized vessel type.
Many nuclear power stations utilize precoat filter/demineralizers for a variety of filtration applications. While precoat filter material has been effective, experience has long ago demonstrated that the use of that material inherently involves several significant disadvantages. The precoat filter medium must be replaced very frequently; its use involves a high ratio of precoat material required to waste filtered, on the order of 10:1, and involves high costs for processing, packaging, shipping and disposing of the material; precoat material requires an extremely large volume of water for backwashing operations, which involve relatively long periods of time.
In precoat filtering systems of the type requiring an expensive pressure vessel, it has long been recognized as desirable to replace the system with a system of the type utilizing permanent filter elements. However, such dismantling or conversion of precoat filter systems has not heretofore been feasible because of the expense involved, especially in nuclear energy facilities. A significant element of this expense is the loss of the pre-existing pressure vessel, the sacrifice of which typically increase the cost of conversion to a permanent filter system to a prohibitive level.